Pumps for pumping molten metal of the type that include a motor driven impeller typically position the impeller on the end of a shaft inside an impeller chamber of an elongated base having an inlet and outlet from the impeller chamber. Upon rotation of the impeller, molten metal is drawn into the base into the impeller chamber and then travels to the outlet of the base. If the pump is a circulation or submerged discharge pump, the outlet of the base extends as a passageway to the outer surface of the base, which circulates the molten metal through a furnace or hearth, for example. If the pump is a transfer pump, the outlet can lead to a riser spaced apart from the shaft, which extends above the pump to a conduit which directs the molten metal to another location such as to a ladle or to a die casting machine. All of the components of the pump that are in the molten metal environment are typically made of refractory material such as graphite, ceramic, graphite with a ceramic covering or graphite impregnated with a refractory oxide.
One type of transfer pump for pumping molten metal is a tube pump that includes no elongated base with impeller chamber and typically has a smaller capacity than such a pump with base. The tube pump includes a refractory tube having upper and lower end portions. A motor is disposed near the upper end portion of the tube. A shaft extends in the tube and is connected to the motor near the upper end portion of the tube. An impeller is connected to the shaft in the lower end portion of the tube. An upper outlet transfer passageway extends from the tube. The tube is open at the upper end portion, for example, to access the coupling between the motor drive shaft and the pump shaft. These tube pumps are used to transfer molten metal from a bath of molten metal that circulates into a furnace, for example to a crucible. During operation, molten metal travels up the tube and out the outlet passageway. These pumps suffer from the disadvantage and danger of overflowing out the top such as when the impeller is rotated too fast. At a minimum, this can damage the coupling between the motor drive shaft and the pump shaft, or can rise into the motor itself damaging it. Molten metal splashing or overflow also presents an extreme hazard of injuring workers. It would be advantageous if these problems and dangers of tube pumps could be avoided.
When the molten metal is added to the crucible it may be transported to a flux station where a rotary degasser (e.g., a submerged rotor rotated on the end of a shaft having a passageway that feeds gas along the shaft and out the rotor) is used to add gas to the molten metal in the crucible. Flux is also added to the surface of the molten metal in the crucible and mixed upon rotation of the rotor. The flux is added to clean the molten metal.
Also, flux is typically added to molten metal circulating through the hearth or furnace by injecting the flux along with a gas stream through a lance operated by hand. The flux is used to clean the molten metal and is typically in particulate form. This process is cumbersome and hazardous to workers who have to be near the molten metal when operating the lance. Attempts to replace the hand lancing of flux addition by designing the pumps so as to receive the flux near the pump or inside the base have not been entirely successful. For example, flux conduits in which inert gas and particulate flux are injected through an inner passageway of the conduit on the order of an inch or less in diameter are ineffective in that they routinely become clogged.
Pumps of the type that include a base have been designed with a refractory shaft sleeve that extends between the motor support plate and the base. The shaft rotates inside the sleeve. Gas has been added into the shaft sleeve as disclosed in U.S. Pat. No. 5,676,520, and displaced the molten metal therein. However, the molten metal does not travel out an upper passage in the shaft sleeve of such a pump, but rather leaves an outlet of the lower base. The longstanding problem of how to effectively introduce flux instead of the hand lancing process remains unsolved with such pumps having bases, as well as with tube pumps having no bases. Moreover, to the knowledge of the inventor, gas has not been directed into the tube of a tube pump.